The present invention relates to a micro-mechanical actuator, and more particularly to a micro-mechanical actuator for moving a micro-element in a micro-electro-mechanical system (MEMS).
A micro-electro-mechanical system (MEMS) pertains to a technique analogous to a semiconductor manufacturing process to produce a tiny and actuated mechanical element. A micro-mechanical actuator utilizing an electrostatic force as the actuating power has various applications. A conventional micro-mechanical actuator is schematically shown in FIGS. 1Axcx9c1C wherein FIGS. 1B and 1C are cross sectional views taken along the line A-Axe2x80x2 of FIG. 1A. In the left portion of the figure, an object 11 supported by anchors 101 is to be actuated to move up and down, and in the right portion, another object 12 supported by anchors 102 is to be actuated to rotate with a shaft 121. For each of the objects 11 and 12, the object itself functions as an electrode which interacts with another electrode 131 or 132 formed on the substrate 14 to control the movement or the rotation of the object 11 or 12, as shown in FIG. 1B. The interaction between the object electrode 11 or 12 and the electrode 131 or 132 is generated due to the electrostatic force therebetween. Owing to the electrostatic attracting force, the top electrode 11 moves toward the bottom electrode 131 as indicated by the arrow B so as to reduce the size of the gap therebetween, as shown in the left portion of FIG. 1C. On the other hand, for the right portion of FIG. 1C, the top electrode 12 moves toward one of the bottom electrodes 132 so as to rotate in a direction indicated by the arrow C.
For the conventional micro-mechanical actuator mentioned as above, the rotation angle is confined within a small range if the gap d is made small. On the contrary, if the gap d is made large, the voltage for actuating the circuit will be required to be large correspondingly so as to load burden on the actuating circuit.
Using a supporting spring device of relatively low elasticity coefficient between each anchor and the object may lower the actuating voltage. The dynamic response of the micro-mechanical actuator, however, will become slow so as to adversely effect the properties of the device.
U.S. patent application No. 5,995,688 discloses a micro-mechanical actuator which enlarges the rotation angle of the object in a single direction without increasing the actuating voltage. Please refer to FIGS. 2Axcx9c2C wherein FIGS. 2B and 2C are cross sectional views taken along the line D-Dxe2x80x2 of FIG. 2A. A micro-mechanical actuator 20 consisting of a top electrode 201 and a bottom electrode 202 is used for actuating an object 21 connected to the top electrode 201. When the top electrode 201 is attracted by the bottom electrode 202 to move downwards, as indicated by an arrow E, the object 21 is levered up, as indicated by the arrow F, because of the presence of a fulcrum 22, as shown in FIG. 2C. Accordingly, the object 21 can be levered up by a relatively large travel. The levering down of the arm 21, however, is still confined by the substrate 24.
Therefore, an object of the present invention is to provide a micro-mechanical actuator for actuating an object in a micro-electro-mechanical system, which allows a relatively large travel range of the object.
The present invention relates to a micro-mechanical actuator for actuating an object in a micro-electro-mechanical system, which includes a substrate for being flexibly connected thereto the object; a first actuating force generator positioned on the substrate for generating a first actuating force; a first auxiliary lever having opposite first and second portions thereof flexibly connected to the first actuating force generator and a first end of the object, respectively, for performing a first levering operation to transmit the object in response to the first actuating force; and a first fulcrum element connected to the first auxiliary lever for allowing the first auxiliary lever to perform the first levering operation thereabout, and arranged at a first specific position for allowing the second portion of the first auxiliary lever has a first shift larger than a second shift of the first portion of the first auxiliary lever in response to the first actuating force.
In an embodiment, the first actuating force generator includes a bottom electrode secured on the substrate; and a top electrode flexibly connected to the first auxiliary lever and the substrate, and moved downwards by an attracting electrostatic force between the top and bottom electrodes to generate the first actuating force for the first auxiliary lever.
Preferably, the first auxiliary lever includes a bump structure for strengthening the first auxiliary lever.
Preferably, the first fulcrum is secured onto the substrate via an anchor.
The first specific position of the first fulcrum may lie between the first and second portions of the first auxiliary lever. Alternatively, the specific position of the first fulcrum may lie at the same side of the first and second portions.
The substrate may be directly connected thereto a second end of the object. Alternatively, the substrate may be connected thereto a second end of the object via a second actuating force generator and a second auxiliary lever. The second actuating force generator is positioned on the substrate for generating a second actuating force. The second auxiliary lever having opposite third and fourth portions thereof flexibly connected to the second actuating force generator and the second end of the object, respectively, for performing a second levering operation to transmit the object in response to the second actuating force. In this embodiment, the micro-mechanical actuator further includes a second fulcrum element connected to the second auxiliary lever for allowing the second auxiliary lever to perform the second levering operation thereabout, and arranged at a second specific position for allowing the fourth portion of the second auxiliary lever has a third shift larger than a fourth shift of the third portion of the second auxiliary lever in response to the second actuating force.
Preferably, the substrate includes a trench positioned right under the first actuating lever and the object for providing a space at least sufficient for the first and second shifts of the first actuating lever.
For example, the micro-mechanical actuator can be used for actuating an optical switch or a radio-frequency (RF) switch in a micro-electro-mechanical system.
In an embodiment, the first auxiliary lever and the first fulcrum are formed by steps of forming a trench and a mask on the substrate; forming a sacrificial layer over the trench; forming a structure layer on the sacrificial layer and the mask; and defining a pattern on the structure layer, and removing the sacrificial layer.
In an embodiment, the substrate is a silicon substrate. The mask is formed of silicon nitride. The sacrificial layer is formed of silicon dioxide. The structure layer is formed of a material selected from a group consisting of silicon nitride, polysilicon and metal.
Preferably, the first auxiliary lever includes a U-shaped cross section extending toward the trench for strengthening the first auxiliary lever.
Preferably, the trench is further enlarged by etching the substrate. For example, the etching of the substrate is performed by anisotropic wet etching after removing the sacrificial layer, or deep reactive ion etching from a side of the substrate opposite to the sacrificial layer before removing the sacrificial layer.
Preferably, the pattern on the structure layer further includes an anchor on the mask for securing the first fulcrum onto the substrate.